This invention relates to seating and sealing means for valves and is particularly concerned with providing means to seal the valve when the primary seal has been destroyed or rendered inoperative by abnormally high temperatures such as may be caused by a fire in the vicinity of the valve. The invention is particularly useful in valves employing a spherical closure member, hereafter referred to as "ball valves" of the type disclosed in U.S. Pat. No. 3,883,112. As shown there, such valves typically employ annular seat rings on either side of the closure member to prevent the leakage of fluid between the closure member and the body when the closure member is in closed position. A relatively resilient annular insert in the seat ring sealingly engages the ball to provide the primary seal with the ball. Usually such inserts are made from nylon, tetrafluoroethylene, or a like hard synthetic plastic material. A secondary sealing means is provided by the seat ring which has a spherical surface conforming to the curvature of the ball and which sealingly engages the ball. This seal is enhanced by the introduction of a flowable plastic lubricant into an annular groove in this surface. The plastic sealant also provides a lubricating function to minimize friction between the seat ring and the ball. A resilient O-ring of rubber or of a like elastomer is provided to seal between the seat ring and the body. Thus, the path between the seat ring and the ball and the path between the seat ring and the body are sealed against leakage.
The arrangement described above provides a reasonably effective seal under normal conditions. However, in the event of a fire near the valve, the resilient seal members which seal between the seat and the ball and the seat and the body would in all probability be subject to thermal damage. In large valves, the metal mass of the valve keeps the temperatures in the seal region low enough during fires of reasonable duration to assure satisfactory sealing performance. However, in smaller valves, non-metallic seals would be destroyed or rendered inoperative. The problem of seal destruction at high temperatures has long been recognized and prior efforts to solve this problem by providing fire resistant seals are shown in the U.S. patents to Allen, U.S. Pat. Nos. 3,346,234, and 3,990,465, and the patent to Calvert, U.S. Pat. No. 4,108,196. The patent to Calvert and both patents to Allen all disclose ball valves having supplementary fire seals. In each case, however, only one seat ring is employed and supplementary metallic seals are urged into sealing engagement between the body and the ring when the normally effective resilient rings are destroyed. In the patent to Allen, U.S. Pat. No. 3,346,234, a metallic ring 32 is urged into sealing engagement between a inclined surface on the seat ring and the body when the resilient, non-metallic rings 28 and 37 are destroyed. Similarly the patent to Allen, U.S. Pat. No. 3,990,465 provides a metallic backup ring 40 which is urged into sealing engagement between the seat and the body when the normally effective resilient seal ring 31 which is formed of teflon is destroyed. In the Calvert patent, "bushes" 15 and 18 are provided between the trunnions which are destructible by fire so that when these bushes are destroyed, the ball valve is allowed to move downstream into sealing engagement with the downstream ring thereby providing a metal to metal seal between the ball and the seat ring on the downstream side of the ball.
U.S. Pat. No. 3,504,885 to Hulsey, while not showing a fire resistant seal ring does show the concept of a separate backup seat ring and seal that limits leakage when the primary seal ring and seat fails. While both patents to Allen and the patent to Calvert do attempt to provide a fire resistant seating-sealing arrangement, they utilize a single seat ring with which the backup sealing ring acts in conjunction to provide a secondary seal in case the primary seal is destroyed. While the use of a single seat ring may be feasible in the larger size valves, in the smaller size valves, any attempt to provide both a primary seal and a secondary seal between the seat ring and the ball and the seat ring and the body renders the seat ring somewhat unnecessarily bulky and complicated. While ball valve seat rings are usually formed of metal, the rings must be able to flex sufficiently to insure an extremely close fit between the ball and the sealing surface on the seat ring. In smaller sized valves excessive bulk in relation to the size of the valve will result in a ring which is not able to flex sufficiently
Accordingly, it is an object of the present invention to provide a seal arrangement for valves which will function even when exposed to elevated temperatures.
It is a more specific object of the present invention to provide a secondary seat ring in addition to the usual conventional seat ring which will provide an effective sealing function in the event the primary or the conventional seat ring and seal fails to function.
It is a further object of this invention to provide dual closely associated seat rings, one of which is effective to seal the ball with respect to the seat ring and the seat ring with respect to the body at elevated temperatures.
It is still another object of this invention to provide a seating-sealing arrangement for a ball valve which is made of fire resistant materials.
Other objects of this invention will appear as the following description proceeds.